Early graphics transfer was achieved with wet transfer decals (see for example U.S. Pat. No. 3,065,120). Wet transfer decals use a release liner coated with a water-soluble composition to carry a transferable water-insoluble lacquer and/or ink image. The water-insoluble image is transferred from the release liner to a receptor by soaking the entire decal in water until the bonding strength of the water-soluble intermediate coating is weakened, removing the water-insoluble graphics from the release liner, and then pressing the removed image onto the receptor.
The use of wet transfer decals declined with the advent of pressure sensitive graphics transfer articles (see for example U.S. Pat. Nos. 3,065,120, 3,276,933, 3,574,049 and 3,708,320). Heat curable graphics transfer articles have also been used for certain purposes. (See for example, U.S. Pat. Nos. 3,907,974 and 3,928,710).
While various methods of graphics transfer may work reasonably well for small graphics, larger sized graphics tend to present additional problems, one of which is application of such a larger sized graphic onto a substrate.
Enlarged reproductions of photographs are used extensively in the advertising and commercial graphics industries to produce photographic signage. These reproduced photographs are commonly mounted onto a sheet of structural material, such as polycarbonate, to display of the photograph. While such photographic displays provide a professional appearance, they tend to be expensive, bulky, subject to delamination of the picture from the structural material, subject to fading-(photographic dyes tend to fade with exposure to UV light), and limited to a display/of the exact subject matter shown in the photograph. In addition, the process requires capital-intensive equipment and is therefore practiced by a limited number of vendors.
Electrostatic printing of computer digitized photographs and other artwork is revolutionizing the manner in which the advertising and commercial graphics industries produce signage. A work of art, such as a photograph, is scanned to produce a digitized color reproduction. The digitized reproduction can be viewed on a video monitor and easily edited as desired. The digitized reproduction can be quickly and efficiently printed by use of an electrostatic color or ink jet printer. Such electrostatically-produced images may be printed directly onto the final imaging film or may be printed onto transfer media and then be transferred from the transfer media onto selected receptors, such as coated vinyl films, for eventual mounting of the imaged laminate onto a display surface, such as a billboard or the side of a semi-trailer. Such electrostatically-produced graphics may be quickly and easily, modified as desired and produce professional signage at a reasonable cost. The graphics-containing receptor can be rolled to facilitate transportation and storage. In addition, with the use of appropriate pressure sensitive adhesives, the mounted graphics are unlikely to peel or delaminate from the display surface.
Graphics intended for exterior display are frequently coated with a protective coating to shield the graphics from environmental damage, such as fading from exposure to ultraviolet light, delamination caused by moisture or humidity, scratching resulting from airborne particles, yellowing caused by pollutants, vandalism, etc. Clear coating has been found to be of significant benefit in increasing the useful life span of graphics and is widely used in the industry. Such protective coatings, commonly/referenced as "clear coats", can be applied by flood coating the finished graphics with a solvent-based solution of the clear coat polymer with evaporation of the solvent. However, solvent-based methods of applying a clear coat suffer several major drawbacks including significant time delays in the manufacture of graphics caused by the need to drive solvent from the clear coat solution, and the various environmental and workplace issues involved in the use and storage of potentially hazardous solvents.
Clear Coat Films
Clear, pressure sensitive films have been used to provide a protective clear coat. However, these films tend to be quite thick since are usually handled as free films. Furthermore, they are more expensive since they often require a special release liner, and they often require a premask to aid in application, which involves yet another manufacturing step. Efforts to further improve durability and/or production efficiency of graphics transfer articles and transfer techniques has focused upon the development of materials using water borne polymers or extended durability materials, but these all require additional manufacturing steps for the consumer.
Alternatively, a clear coat can be provided using the method described in U.S. Pat. No. 4,737,224, wherein the clear coat is a dry thermally transferable ink composition. The clear coat is transferred by placing the clear coat composition on a vacuum frame and evacuating substantially all of the air from an interface between the clear coat and a receptor. The pressure is maintained and the clear coat composition is heated sufficiently (typically in the range of 167.degree. F. to 230.degree. F.) to soften the clear coat composition and fuse the composition to the receptor.
Premasking Steps
After the graphics are produced by any imaging method, they are typically laminated with a "premask", which is usually a pressure sensitive adhesive coated paper. Ideally, this paper is translucent, for better visibility and low cost. The purpose of the premask is to enhance the rigidity of the graphic to facilitate application. Accordingly, a substantial need exists for a graphics transfer article and processing techniques that permits the transfer of commercially acceptable graphics from a graphics transfer article onto a wide range of receptor materials while reducing the use of volatile solvents used in the process and minimizing the number of steps required by the user.